So has the US Public Health Service
Here is some great information to explain why, and what to do about it:

Allergens & Irritants Guide

http://www.niehs.nih.gov/health/topics/agents/allergens/

Guide to Common Allergies

http://www.treeremoval.com/tree-pollen-and-other-common-allergies/

Skin Allergies

http://acaai.org/allergies/types/skin-allergies
I would add to this section that in general I don’t find the skin scratch tests useful for ingested allergens. The very best test to figure out food allergens (not necessarily a full blown anaphylactic reaction, but hives or GI disturbance or even mood changes can be caused by food irritants) is the MRI/LEAP test. Learn more at www.NOWLEAP.com

The Guide to Animal and Insect Allergen-Free Homes

http://www.cleanitsupply.com/t/The_Guide_to_Animal_and_Insect_Allergen-Free_Homes.aspx

Food Allergies and Eczema

http://nationaleczema.org/eczema/types-of-eczema/atopic-dermatitis-2/food-allergies/